TIGIT and hepatocellular carcinoma: Circular RNA cell division cycle and apoptosis regulator 1 (circCCAR1), as exosomes, released by HCC cells are taken up by CD8+ T cells, which can inhibit the proliferation of activated CD8+ T cells, promote their apoptosis, reduce their cytotoxicity and cytokine secretion capacity, and up-regulate the expression of LAG-3, PD-1, TIM-3 and TIGIT on their surface, inducing CD8+ T cell dysfunction.